1. Field of the Invention
The present invention relates to an electrochemical device which can be employed, for example as a battery, an electrochromic device, and a condenser.
2. Discussion of Background
Recently there is a great demand for a solidified electrochemcial device which uses an electrochemical reaction. Since conventional devices which use electrochemical reactions, such as batteries and electrochromic elements, employ an electrolyte solution, they have problems in the operational reliability as caused by the leakage and evaporation of the electrolyte solution. In order to eliminate such problems and improve the operational reliability of the devices, there have been proposed the gelation of an electrolyte solution as in Japanese Laid-Open Patent Application 62-5506 and the solidification of the same as in Japanese Laid-Open Patent Application 63-58704.
Furthermore, a polymeric solid electrolyte having high ionic conductivity has been reported in Polymer, 14, 589 (1973).
Recently polymeric solid electrolytes which do not contain a solvent are actively studied, by which the above-mentioned conventional problems are expected to be solved. However, since a gelled electrolyte lacks mechanical strength, when it is employed in a thin device, the problem of the short-circuit between electrodes is apt to occur or the device itself is broken while in use. Therefore such a gelled electrolyte is not suitable for use in thin devices.
Conventional polymeric solid electrolytes having high ionic conductivity are generally so soft that they lack self-supporting property. Therefore such polymeric solid electrolytes have the same problems as those of the gelled electrolyte. Furthermore, with respect to such polymeric solid electrolytes, it is a significant problem to be solved to make the polymeric solid electrolytes in the form of a thin film in order to reduce the internal resistance of the device.
In order to eliminate the above-mentioned problems including the short-circuit between the electrodes, it has been proposed to integrate a porous material and a filler in a solid electrolyte as disclosed, for example, in Japanese Laid-Open Patent Applications 60-195878 and 60-165058. This method, however, has the shortcoming that an electrolyte layer with a uniform thickness cannot be obtained, so that when the electrolyte layer is employed in an electrochromic device, the colors produced in the electrochromic device becomes ununiform or the operational reliability is decreased while in repeated use.
In addition to the above method, there is a method of depositing a polyethylene oxide on a substrate serving as an electrode. This method makes it possible to make the solid electrolyte sufficiently thin uniformly, but has the shortcomings that the deposition of the polyethylene oxide itself is difficult, and minute short-circuits take place when an electrolyte film having a large area is used.
With respect to batteries, a demand for a solid-like, thin battery is increasing. However, a uniformly thin electrolyte layer for use in a solid-like thin battery cannot be satisfactorily prepared by the conventional methods.